The objection is vigorously urged that Herod was a rex socius — an allied king, and that all taxes in his dominion must, therefore, have been levied by himself. But it is difficult to see how Herod was entitled, in fact, to be called a rex socius, since the term means one allied, in commercial language, a partner. Herod was wholly the creature of Augustus; originally set as king, not as having any hereditary claims or being even of Jewish descent, but because he could be a useful instrument in the hands of the Romans. He was hated of the Jews both as an alien and as of a cruel and despotic nature, and he held the throne ouly through the fear which the Roman support inspired. Josephus mentions many instances, showing how far he was subjected all his reign to the emperor and to his representatives, the governors of Syria. A clear proof of this is seen in the fact that the Jews were forced to take the oath of allegiance to Augustus as well as to Herod. (Joseph., Antiq., xvii. 2. 4.)
To say, then, that Augustus would, from regard to any royal rights of Herod, make him an exception, and not carry out his general policy of taxation in his dominions, is to make the Roman ruler a constitutional monarch and to attribute to him a softness of disposition which is indicated by no other acts of his public life. And there may have been special reasons why, before the death of Herod, known to be near his end, and his sons quarreling about the succession, Augustus should have had this enrollment made; for he must have foreseen the probability, if he had not already formed the determination, that his kingdom should speedily be made a Roman province.
Adapted from The Life of Our Lord upon the Earth by Samuel James Andrews.